PROJECT REPORT ON A NOVEL REAR END COLLISION & ACCIDENT AVOIDANCE SYSTEM WITH DYNAMIC SPEED GOVERNOR
ABSTRACT Automotive vehicles are increasingly being equipped with collision avoidance and warning systems for predicting the potential collision with an external object, such as another vehicle or a pedestrian. Upon detecting a potential collision, such systems typically initiate an action to avoid the collision and/or provide a warning to the vehicle operator. This system consist of a distance-measuring system based on ultrasonic sound utilizing the PIC 16f877A microcontroller and transmits a burst of ultrasonic sound waves towards the target and then receives the corresponding echo. An ultrasonic sound sensor is used to detect the arrival of the echo to the system. The time taken for the ultrasonic burst to travel the distance from the system to the subject and back to the system is accurately measured by the microcontroller. It also provides a warning signal to the driver if the distance between vehicle and obstacle crosses a particular limit. It also monitors the speed of the vehicle and if the speed limit is exceeded it is informed to the driver. The speed limit for different class of vehicles is set by authorities at different.
1. INTRODUCTION This report describes a distance-measuring system based on ultrasonic sound utilizing the PIC 16f877A microcontroller. With the help of the distance measured, the micro-controller will make the vehicle stop suddenly if the vehicle is about to hit any obstacle or any other vehicle. With the help of this technology accidents are avoided. The system transmits a burst of ultrasonic sound waves towards the target and then receives the corresponding echo. An ultrasonic sound sensor is used to detect the arrival of the echo to the system. The time taken for the ultrasonic burst to travel the distance from the system to the subject and back to the system is accurately measured by the microcontroller. Different types of vehicle speed limiters are in current use for regulating traffic especially across roads near populated areas such as hospitals, malls and schools. This project “DYNAMIC SPEED GOVERNER” is a new method by which vehicle speed is controlled externally rather than internally. The speed measurement and control is accomplished via two PIC16F877As with a RF transmitter and a receiver.
SOFTWARE SPECIFICATION MPLAB IDE MPLAB Integrated Development Environment (IDE) is a free, integrated toolset for the development of embedded applications employing Microchip‟s PIC and dsPIC microcontrollers. MPLAB IDE runs as a 32-bit application on MS Windows, is easy to use and includes a host of free software components for fast application development and supercharged debugging. MPLAB IDE also serves as a single, unified graphical user interface for additional Microchip and third party software and hardware development tools. Moving between tools is a snap, and upgrading from the free software simulator to hardware debug and programming tools is done in a flash because MPLAB IDE has the same user interface for all tools. A development system for embedded controllers is a system of programs running on a desktop PC to help write, edit, debug and program code- the intelligence of embedded systems applications in to a microcontroller. MPLAB IDE, runs on a PC and contains all the components needed to design and deploy embedded systems applications. MPLAB IDE Programmer‟s Editor helps write correct code with the language tools of choice. The editor is aware of the assembler and compiler programming constructs and automatically “color-keys” the source code to help ensure it is syntactically correct. The Project Manager enables you to organize the various files used in your application source files,processor description header files and library files. Language tools run into errors when building the application, the offending line is shown and can be “double-clicked” to go to the corresponding source for immediate editing. After editing, press the “build” button to try again. Often this write-compile-fix loop is done many times for complex code, as the subsections are written and tested.
Once the code builds with no errors, it needs to be tested. MPLAB IDE has components called “debuggers” and free software simulators for all PICmicro and PIC devices to help test the code. Even if the hardware is not yet finished, you can begin testing the code with the simulator, a software program that simulates the execution of the microcontroller. Once the hardware is in a prototype stage, a hardware debugger, such as MPLAB ICE or MPLAB ICD 2 can be used. These debuggers run the code in real time on your actual application. The MPLAB ICE physically replaces the microcontroller in the target using a high-speed probe to give you full control over the hardware in your design. The MPLAB ICD 2 uses special circuitry built into many Microchip MCUs with Flash program memory and can “see into” the target microcontrollers program and data memory. The MPLAB ICD 2 can stop and start program execution, allowing you to test the code with the microcontroller in place on the application. After the application is running correctly, you can program a microcontroller with one of Microchip‟s device programmers, such as PICSTART Plus or MPLAB PM3. These programmers verify that the finished code will run as designed. MPLAB IDE supports most PICmicro MCUs and every PIC Digital Signal Controller. How MPLAB IDE Helps The organization of MPLAB IDE tools by function helps make pull-down menus and customizable quick keys easy to find and use. MPLAB IDE tools allow us to Assemble, compile, and link source code. Debug the executable logic by watching program flow with the simulator, or in real time with the MPLAB-ICE emulator. Make timing measurements, view variables in watch windows, program firmware with PICSTART Plus or PRO MATE II, find quick answers to questions from the MPLAB IDE on-line Help and much more. MPLAB IDE – An Integrated Development Environment
MPLAB IDE is an easy-to-learn and use Integrated Development Environment (IDE). The IDE provides firmware development engineers the flexibility to develop and debug
firmware for Microchip‟s PICmicro MCU families. The MPLAB IDE runs under Microsoft Windows 3.1x, Windows 95/98, Windows NT, or Windows 2000. MPLAB IDE provides functions that allow you to: 1.Create and Edit Source Files 2.Group Files into Projects 3.Debug Source Code 4.Debug Executable Logic Using the Simulator or Emulator(s) The MPLAB IDE allows you to create and edit source code by providing you with a full-featured text editor. Further, you can easily debug source code with the aid of a Build Results window that displays the errors found by the compiler, assembler, and linker when generating executable files. A Project Manager allows you to group source files, precompiled object files, libraries, and linker script files into a project format. The MPLAB IDE also provides feature-rich simulator and emulator environments to debug the logic of executables. Some of the features are a variety of windows allowing you to view the contents of all data and program memory locations source code, program memory and absolute listing windows allowing you to view the source code and its assembly-level equivalent separately and together.
CCS C COMPILER The compiler contains Standard C operators and built in libraries that are specific to the PIC registers. Access to hardware features from C. The compiler includes built-in functions to access the PIC microcontroller hardware such as READ_ADC to read a value from the A/D converter. Discrete I/O is handled by describing the port characteristics in a PRAGMA. Functions such as INPUT and OUTPUT_HIGH will properly maintain the tri-state registers. Variables including structures may be directly mapped to memory such as I/O ports to best represent the hardware structure in C. The microcontroller clock speed may be specified in a PRAGMA to permit built in functions to delay for a given number of microseconds or milliseconds. Serial I/O functions allow standard functions such as GETC and PRINTF to be used for RS-232 like I/O. The compiler runs under Windows 95, 98, ME, NT4, 2000, XP, Vista or Linux. It outputs hex and debug files that are selectable and compatible with popular emulators and programmers including the MPLAB IDE for source level debugging. Functions may be implemented inline or separate, allowing to optimize for either ROM concerns or speed concerns. Function parameters are passed in reusable registers. Inline functions with reference parameters are implemented efficiently with no memory overhead. During the linking process the program structure, including the call tree, is analyzed. Functions that call one another frequently are grouped together in the same page segment. Functions may be implemented inline or separate. RAM is allocated efficiently by using the call tree to determine how locations can be re-used. Constant strings and tables are saved in the device ROM.
CAD SOFT – EAGLE Fig.1.1: Cad soft-eagle
EAGLE (Easily Applicable Graphical Layout Editor) is a proprietary ECAD program produced by Cad Soft in Germany (American marketing division: Cad Soft USA). It is very commonly used by private electronics enthusiasts, because there is a free limited version for non-profit use and it is available in English and German. Cad Soft has released versions for Microsoft Windows, Linux, and Mac OS X.
Fig.1.2. Eagle soft
EAGLE contains a schematic editor, for designing circuit diagrams and a PCB layout editor, which allows back annotation to the schematic. EAGLE includes a basic but functional autorouter, or alternatively manual routing can be performed. PCBs designed in EAGLE are accepted by a large amount of PCB fabrication houses without the need to export. EAGLE is very popular with hobbyists because both a basic free edition (with a lower feature set) and a low cost non-profit edition are available.
Schematic capture or schematic entry is a step in the design cycle of electronic design automation (EDA) at which the electronic diagram, or electronic schematic of the designed electronic circuit is created by a designer. This is done interactively with the help of a schematic capture tool also known as schematic editor.
The circuit design is the very first step of actual design of an electronic circuit. Typically sketches are drawn on paper, and then entered into a computer using a schematic editor. Therefore schematic entry is said to be a front-end operation of several others in the design flow.
Despite the complexity of modern components – huge ball grid arrays and tiny passive components – schematic capture is easier today than it has been for many years. CAD software is easier to use and is available in full-featured expensive packages, very capable mid-range packages that sometimes have free versions and completely free versions that are either open source or directly linked to a printed circuit board fabrication company.
In past years, schematic diagrams with largely discrete components were fairly readable however with the newer high pin-count parts and with the almost universal use of standard letter-sized paper, schematics have become less so. Many times, there will be a single large part on a page with nothing but pin reference keys to connect it to other pages.
LITERATURE REVIEW The new speed limiting system presented in this project combines several pioneering techniques that integrate wireless technologies in order to implement a reliable speed control system. This proposed system can be easily implemented near different populated areas. The power of the proposed system lies in its flexibility and capability of development with little hardware changes such as changing the speed limits and speed control methods using the software of the base station in negligible amount of time. The proposed system is based on microcontroller technology for collecting data related to speed and transmitting it through a transceiver to a base station that analyzes the transmitted data and takes appropriate decisions related to speed limit and control requirements. Speed Governor regulates the top speed and/or maximum rpm of a vehicle, whether it is electronically or mechanical. The governor is emplaced by the manufacturer to meet laws of the nation is which the vehicle will be sold, protect the drivers from operating at unsafe speed, or to protect the car from being driving beyond its physical or mechanical threshold
CHAPTER-2 BLOCK DAIGRAM TRANSMITTER
Micro controller PIC 16F877A
RF ENCODER
RF TRANSMITTER
RECEIVER
MICRO CONTROLLER
USS TRANSMITER
USS RECEIVER
3 STAGE AMPLIFIERS
COMPARATOR
THE MOTOR
USS RECEIVER
ALARM SECTION
RF DECODER
RF RECEIVER
BLOCK DAIGRAM EXPLANATION MICROCONTROLLER - PIC 16F877A The microcontroller is a set of digital logic circuits integrated on a single silicon „chip‟ whose connections and behavior can be specified and later alter when required, by the program in its memory. The great advantage of this is that in order to change the circuit‟s structure and operation, all that is needed is a change in the program very little, if any, circuit hardware modifications are necessary. The microcontroller unit used here is a PIC16f877A .The core controller is a mid-range family having a built-in SPI master. 16F877A have enough I/O lines for current need. It is capable of initiating all intersystem communications. The master controller controls each functions of the system with a supporting device. Also responsible for reception of commands from the host and taking necessary actions. PIC16F877A is an 8-bit, fully static, EPROM/EPROM/ROM-based CMOS microcontroller. It employs RISC architecture with only 35 word/single cycle instructions. All these instructions are single cycle (1ms) expect for program branches which takes two cycles. The PIC16f877A products are supported by a full featured macro assembler, a software simulator, „C‟ compiler etc. CORE FEATURES: • High performance RISC CPU • Only 35 single word instructions to learn • All single cycle instructions except for program branches which are two cycle • Operating speed: DC - 20 MHz clock input DC - 200 ns instruction cycle • Up to 8K x 14 words of FLASH Program Memory, Up to 368 x 8 bytes of Data Up to Memory (RAM) 256 x 8 bytes of EEPROM Data Memory • Pin out compatible to the PIC16C73B/74B/76/77 • Interrupt capability (up to 14 sources)
• Eight level deep hardware stack
• Programmable code protection • Power saving SLEEP mode • Selectable oscillator options • Low power, high speed CMOS FLASH/EEPROM technology • Fully static design • In-Circuit Serial Programming (ICSP) via two pins • Single 5V In-Circuit Serial Programming capability • In-Circuit Debugging via two pins • Processor read/write access to program memory • Wide operating voltage range: 2.0V to 5.5V • High Sink/Source Current: 25 mA • Commercial, Industrial and Extended temperature ranges • Low-power consumption: - < 0.6 mA typical @ 3V, 4 MHz - 20 μA typical @ 3V, 32 kHz - < 1 μA typical standby current PERIPHERAL FEATURES: • Timer0: 8-bit timer/counter with 8-bit prescaler • Timer1: 16-bit timer/counter with prescaler, can be incremented during SLEEP via external crystal/clock • Timer2: 8-bit timer/counter with 8-bit period register, prescaler and postscaler • Two Capture, Compare, PWM modules - Capture is 16-bit, max. Resolution is 12.5 ns - Compare is 16-bit, max. Resolution is 200 ns - PWM max. Resolution is 10-bit • 10-bit multi-channel Analog-to-Digital converter • Synchronous Serial Port (SSP) with SPI (Master mode) and I2C (Master/Slave) • Universal Synchronous Asynchronous Receiver Transmitter (USART/SCI) with 9-bit address detection • Parallel Slave Port (PSP) 8-bits wide, with external RD, WR and CS controls (40/44-pin only)
• Brown-out detection circuitry for Brown-out Reset (BOR) ANALOG FEATURES: •10-bit, up to 8-channel Analog-to-Digital Converter (A/D) •Brown-out Reset (BOR) •Analog Comparator module with: -Two analog comparators -Programmable on-chip voltage reference (VREF) module -Programmable input multiplexing from device inputs and internal voltage reference -Comparator outputs are externally accessible SPECIAL MICROCONTROLLER FEATURES: •100,000 erase/write cycle Enhanced Flash program memory typical •1,000,000 erase/write cycle Data EEPROM memory typical •Data EEPROM Retention > 40 years •Self-reprogrammable under software control •In-Circuit Serial Programming™ (ICSP™) via two pins •Single-supply 5V In-Circuit Serial Programming •Watchdog Timer (WDT) with its own on-chip RC oscillator for reliable operation •Programmable code protection •Power saving Sleep mode •Selectable oscillator options •In-Circuit Debug (ICD) via two pins MEMORY ORGANIZATION There are three memory blocks in each of the PIC16F87X MCUs. The Program Memory and Data Memory have separate buses so that concurrent access can occur. PROGRAM MEMORY ORGANIZATION
The PIC16F87X devices have a 13-bit program counter capable of addressing an 8K x 14 program memory space. The PIC16F877/876 devices have 8K x 14 words of FLASH program memory, and the PIC16F873/874 devices have 4K x 14. Accessing a location above the
physically implemented address will cause a wraparound. The RESET vector is at 0000h and the interrupt vector is at 0004h. DATA MEMORY ORGANIZATION The data memory is partitioned into multiple banks which contain the General Purpose Registers and the Special Function Registers. Bits RP1 (STATUS<6>) and RP0 (STATUS<5>) are the bank select bits. Each bank extends up to 7Fh (128 bytes). The lower locations of each bank are reserved for the Special Function Registers. Above the Special Function Registers are General Purpose Registers, implemented as static RAM. All implemented banks contain Special Function Registers. Some frequently used Special Function Registers from one bank may be mirrored in another bank for code reduction and quicker access. I/O PORTS Some pins for these I/O ports are multiplexed with analternate function for the peripheral features on the device. In general, when a peripheral is enabled, that pin may not be used as a general purpose I/O pin. Additional information on I/O ports may be found in the PICmicro™ Mid-Range Reference Manual (DS33023). PORTA and the TRISA Register PORTA is a 6-bit wide, bidirectional port. The corresponding data direction register is TRISA. Setting a TRISA bit (= 1) will make the corresponding PORTA pin an input (i.e., put the corresponding output driver in a High-Impedance mode). Clearing a TRISA bit (= 0) will make the corresponding PORTA pin an output (i.e., put the contents of the output latch on the selected pin). All write operations are read-modify-write operations. Therefore, a write to a port implies that the port pins are read, the value is modified and then written to the port data latch. Pin RA4 is multiplexed with the Timer0 module clock input to become the RA4/T0CKI pin. The RA4/T0CKI pin is a Schmitt Trigger input and an open-drain output. All other PORTA pins have TTL input levels and full CMOS output drivers. Other PORTA pins are multiplexed with analog inputs and the analog VREF input for both the A/D converters and the comparators
The operation of each pin is selected by clearing/setting the appropriate control bits in the ADCON1 and/or CMCON registers. PORTB and the TRISB Register PORTB is an 8-bit wide, bidirectional port. The corresponding data direction register is TRISB. Setting a TRISB bit (= 1) will make the corresponding PORTB pin an input (i.e., put the corresponding output driver in a High-Impedance mode). Clearing a TRISB bit (= 0) will make the corresponding PORTB pin an output (i.e., put the contents of the output latch on the selected pin). Three pins of PORTB are multiplexed with the In-Circuit Debugger and Low-Voltage Programming function: RB3/PGM, RB6/PGC and RB7/PGD. The alternate functions of these pins are described in “Special Features of the CPU”. Each of the PORTB pins has a weak internal pull-up. A single control bit can turn on all the pull-ups. This is performed by clearing bit RBPU (OPTION_REG<7>). The weak pull-up is automatically turned off when the port pin is configured as an output. The pull-ups are disabled on a Power-on Reset. PORTC and the TRISC Register PORTC is an 8-bit wide, bidirectional port. The corresponding data direction register is TRISC. Setting a TRISC bit (= 1) will make the corresponding PORTC pin an input (i.e., put the corresponding output driver in a High-Impedance mode). Clearing a TRISC bit (= 0) will make the corresponding PORTC pin an output (i.e., put the contents of the output latch on the selected pin). PORTC is multiplexed with several peripheral functions . PORTC pins have Schmitt Trigger input buffers. When the I2C module is enabled, the PORTC<4:3> pins can be configured with normal I2C levels, or with SMBus levels, by using the CKE bit (SSPSTAT<6>). When enabling peripheral functions, care should be taken in defining TRIS bits for each PORTC pin. Some peripherals override the TRIS bit to make a pin an output, while other peripherals override the TRIS bit to make a pin an input. Since the TRIS bit override is in effect while the peripheral is enabled, read-modify-write instructions (BSF, BCF, XORWF) with TRISC as the destination, should be avoided. The user should refer to the corresponding peripheral section for the correct TRIS bit settings.
PORTD and TRISD Registers PORTD is an 8-bit port with Schmitt Trigger input buffers. Each pin is individually configurable as an input or output. PORTD can be configured as an 8-bit wide microprocessor port (Parallel Slave Port) by setting control bit, PSPMODE (TRISE<4>). In this mode, the input buffers are TTL. PORTE and TRISE Register PORTE has three pins (RE0/RD/AN5, RE1/WR/AN6 and RE2/CS/AN7) which are individually configurable as inputs or outputs. These pins have Schmitt Trigger input buffers. The PORTE pins become the I/O control inputs for the microprocessor port when bit PSPMODE (TRISE<4>) is set. In this mode, the user must make certain that the TRISE<2:0> bits are set and that the pins are configured as digital inputs. Also, ensure that ADCON1 is configured for digital I/O. In this mode, the input buffers are TTL. Register 4-1 shows the TRISE register which also controls the Parallel Slave Port operation. PORTE pins are multiplexed with analog inputs. When selected for analog input, these pins will read as „0‟s. TRISE controls the direction of the RE pins, even when they are being used as analog inputs. The user must make sure to keep the pins configured as inputs when using them as analog inputs. The system has two interconnected modules as its working elements.
RF ENCODER – HT12E The 2^12 encoders are a series of CMOS LSIs for remote control system applications. They are capable of encoding information which consists of N address bits and 12_N data bits. Each address/ data input can be set to one of the two logic states. The programmed addresses/data are transmitted together with the header bits via an RF or an infrared transmission medium upon receipt of a trigger signal. The capability to select a TE trigger on the HT12E or a DATA trigger on the HT12A further enhances the application flexibility of the 2^12 series of encoders. The HT12A additionally provides a 38 kHz carrier for infrared systems. Features
Operating voltage 2.4V~12V for the HT12E
Low power and high noise immunity CMOS technology
Low standby current: 0.1_A (typ.) at VDD=5V
HT12A with a 38kHz carrier for infrared transmission medium
Minimum transmission word
o Four words for the HT12E
o One word for the HT12A
Built-in oscillator needs only 5% resistor
Data code has positive polarity
Minimal external components
HT12A/E: 18-pin DIP/20-pin SOP package.
Applications
Burglar alarm system
Smoke and fire alarm system
Garage door controllers
Car door controllers
Car alarm system
Security system
Cordless telephones
Other remote control systems
Operation The 212 series of encoders begin a 4-word transmission cycle upon receipt of a
transmission enable (TE for the HT12E or D8~D11 for the HT12A, active low). This cycle will
repeat itself as long as the transmission enable (TE or D8~D11) is held low. Once the
transmissions enable returns high the encoder output completes its final cycle and then stops as
shown below.
RF TRANSMITTER The RF Transmitter is ideal for remote control applications where low cost and longer range is required. The transmitter operates from a 1.5 to 12v supply, making it ideal for battery-powered applications. The transmitter employs a SAW stabilized oscillator, ensuring accurate frequency control for best range performance. Output power and harmonic emissions are easy to control. The manufacturing friendly SMT style package and low cost make the RF module make it suitable for high volume applications. RF Transmitter General Features
Low cost
Small size
Frequency range is 433.92 MHz
Out put power 4 to 12 Dbm
It uses ASK modulation
It will transmit up to 100M
RF RECEIVER The RF Receiver we are using is ideal for short-range remote control applications where cost is a primary concern. The receiver module requires no external RF components except for the antenna. It generates virtually no emissions. The super regenerative design exhibits exceptional sensitivity at a very low cost. A SAW filter can be added to the antenna input to improve selectivity for applications that require robust performance. The friendly SIP style package and low-cost make it suitable for high volume applications. RF Receiver General Features
Low cost
No external parts are required
Receiver frequency 433 MHz
Typical sensitivity 105 Dbm
Supply current 2.3mA
Operating voltage 5v
Easy for application
WORKING OF THE SYSTEM
The dynamic speed governor consist of mainly two parts:- the transmitter and
receiver. The system is mainly based on micro controller technology for collecting data related to
speed and transmits the data to the micro controller using RF communication. The micro
controller analyses the transmitted data and takes appropriate decisions related to speed limit and
control requirements.
The dynamic speed governor will be needed in populated areas such as hospitals,
malls and schools for regulating traffic. The RF transmitter of the system is mounted on the
signal board and the micro controller of the transmitter part always sense the speed limit of the
area for that the speed limit will be stored in the micro controller. The speed limit of the vehicle
will be transmitted using RF transmitter to the approaching vehicles.
An RF receiver is kept inside the vehicle and the receiver accepts the incoming
signals and then feeds the limit of speed as an input to a comparator. An RPM meter is used to
transform the mechanical rotational movement of the vehicle into an electrical signal and using
this method the speed of the approaching vehicle can be detected. This calculated speed from the
RPM meter is given to the next input pin of the comparator.
At the comparator both speed given to the both input pin is compared and if the
speed of the vehicle is greater than the speed limit the controller will reduce the speed of the
vehicle to the limit by using PWM characteristic of the micro controller.
RF DECODER – HT12D The 2^12 decoders are a series of CMOS LSIs for remote control system applications. They are paired with Holtek_s 212 series of encoders (refer to the encoder/decoder cross reference table). For proper operation, a pair of encoder/decoder with the same number of addresses and data format should be chosen. The decoders receive serial addresses and data from a programmed 212 series of encoders that are transmitted by a carrier using an RF or an IR transmission medium. They compare the serial input data three times continuously with their local addresses. If no error or unmatched codes are found, the input data codes are decoded and then transferred to the output pins. The VT pin also goes high to indicate a valid transmission. The 2^12 series of decoders are capable of decoding informations that consist of N bits of address and 12_N bits of data. Of this series, the HT12D is arranged to provide 8 address bits and 4 data bits, and HT12F is used to decode 12 bits of address information. Features
Operating voltage: 2.4V~12V
Low power and high noise immunity CMOS technology
Low standby current
Capable of decoding 12 bits of information
Binary address setting
Received codes are checked 3 times
Address/Data number combination
HT12D: 8 address bits and 4 data bits
HT12F: 12 address bits only
Built-in oscillator needs only 5% resistor
Valid transmission indicator
Easy interface with an RF or an infrared transmission medium
Minimal external components
Pair with Holtek_s 212 series of encoders
18-pin DIP, 20-pin SOP package
Applications
Burglar alarm system
Smoke and fire alarm system
Garage door controllers
Car door controllers
Car alarm system
Security system
Cordless telephones
Other remote control systems
Operation
The 212 series of decoders provides various combinations of addresses and data
pins in different packagesso as to pair with the 212 series of encoders. The decoders receive data
that are transmitted by an encoder and interpret the first N bits of code period as addresses and
the last 12_N bits as data, where N is the address code number. A signal on the DIN pin activates
the oscillator which in turn decodes the incoming address and data. The decoders will then check
the received address three times continuously. If the received address codes all match the
contents of the decoder_s local address, the 12_N bits of data are decoded to activate the output
pins and the VT pin is set high to indicate a valid transmission. This will last unless the address
code is incorrect or no signal is received. The output of the VT pin is high only when the
transmission is valid. Otherwise it is always low.
Output type
Of the 212 series of decoders, the HT12F has no data output pin but its VT pin
can be used as a momentary data output. The HT12D, on the other hand, provides 4 latch type
data pins whose data remain unchanged until new data are received.
Notes: Data type: L stands for latch type data output. VT can be used as a momentary data
output.
Flowchart
The oscillator is disabled in the standby state and activated when a logic _high_
signal applies to the DIN pin.
That is to say, the DIN should be kept low if there is no signal input.
ULTRASONIC SENSORS
Ultrasonic sensors are commonly used for a wide variety of noncontact presence,
proximity, or distance measuring applications. These devices typically transmit ultrasonic sound
toward a target, which reflects the sound back to the sensor. The system then measures the time
for the echo to return to the sensor and computes the distance to the target using the speed of
sound in the medium.
The wide varieties of sensors currently on the market differ from one another in
their mounting configurations, environmental sealing, and electronic features. Acoustically, they
operate at different frequencies and have different radiation patterns. It is usually not difficult to
select a sensor that best meets the environmental and mechanical requirements for a particular
application, or to evaluate the electronic features available with different models.
The principle of working of an ultrasonic sensor is easy. The sensor transmits ultrasonic sound
waves and waits for reflected sound waves. After receiving reflected sound wave or usually
named echo, sensor detects the distance in different ways. Triggered the sensor and then wait for
echo pulse. Measuring echo pulse width is important for us because 30 μs means us 1 cm.
Ultrasonic Ranging System
The development of applications using ultrasonic sensors requires good
understanding of its operating principles and its interaction with the environment. They rely on
the principle of time of flight or propagation of sound waves in air. The system either measures
the echo reflection of the sound from the object (in case where the transmitter and the receiver is
on the same device) or the time of flight of the sound wave from the transmitter to the receiver
(in case either the transmitter or the receiver is mounted on the object).
Ultrasonic Transmitter
The transmitter consists of an electronics circuitry and an electromechanical
transducer. The electronic circuitry generates the required frequency electrical signal and the
electromechanical transducer converts that electrical signal into the physical form and activates
the open medium surface. This oscillating physical surface creates the ultrasonic waves. The
oscillating surface creates a pressure variation and ultimately a pressure wave with a frequency
equal to that of the surface oscillation. The figure below shows the generation of ultrasonic
waves.
Ultrasonic Receiver
The receiver also has the same configuration except that it has a receiver electronic
circuitry and a transducer, which converts the ultrasonic sound waves into an electrical signal.
The sound waves travel into the medium and are reflected by an object in the path of the waves.
This reflected wave is then sensed by the receiver, which actually calculates the time of flight of
the signal to find the distance.
Transmitter and Receiver pair
It consists of a transmitter and receiver pair on the device. There are two different
transducers for transmitter and receiver. The transmitter transmits and the receiver waits for the
reflected signals. The following figure illustrates the transmitter/receiver pair.
LCD MODULE The LCD module is a parallel interface sixteen pin module. The first three pins of LCD module are used for contrast adjusting. Here the first pin is connected to ground, second to the voltage supply and third to the variable resistor. The pins, seven to fourteen are data lines (D0 to D7). In this particular circuit the data lines D4 to D7 are used because the LCD driver available is 4 line data bus. 15th pin is connected to the 5 volt supply. Pin 4, 5, 6 are control pins, R/W, RS and enable respectively. 16th pin is connected to the ground through a transistor. The voltage from pic16f877a turn on the transistor and it in turn turns on the LCD backlight .Resistor R9 controls the voltage supplied to the transistor. PINOUT LCD modules may have a parallel or serial interface. The module discussed here has a 14-pin parallel interface. The pin out for this module is shown below. Enable (E) This line allows access to the display through R/W and RS lines. When this line is low, the LCD is disabled and ignores signals from R/W and RS. When (E) line is high, the LCD checks the state of the two control lines and responds accordingly. Read/Write (R/W) This line determines the direction of data between the LCD and microcontroller. When it is low, data is written to the LCD. When it is high, data is read from the LCD. Register select (RS) with the help of this line, the LCD interprets the type of data on data lines. When it is low, an instruction is being written to the LCD. When it is high, a character is being written to the LCD.
Contrast: A variable voltage applied to this pin controls the contrast. Use a potentiometer and adjust until you see the background. DB0-DB7: Apply the data or commands to these pins.
Reading data from the LCD is done in the same way, but control line R/W has to be high. When we send a high to the LCD, it will reset and wait for instructions. Typical instructions sent to LCD display after a reset are: turning on a display, turning on a cursor and writing characters from left to right. When the LCD is initialized, it is ready to continue receiving data or instructions. If it receives a character, it will write it on the display and move the cursor one space to the right. The Cursor marks the next location where a character will be written. When we want to write a string of characters, first we need to set up the starting address, and then send one character at a time. Characters that can be shown on the display are stored in data display (DD) RAM. The size of DDRAM is 80 bytes.
The LCD display also possesses 64 bytes of Character-Generator (CG) RAM. This memory is used for characters defined by the user. Data in CG RAM is represented as an 8-bit character bit-map. Each character takes up 8 bytes of CG RAM, so the total number of characters, which the user can define, is eight. In order to read in the character bit-map to the LCD display, we must first set the CG RAM address to starting point (usually 0), and then write data to the display.
R2
1.2K C4
103
C1
100uF/16V
D3
LED
J1
CON3
1
2
3
0
+5 VCC
U1
LM7805C/TO220
1 3
2
IN OUT
GND
D2
1N4007 C3
1000uF/25V
C2
104
+12v
POWER SUPPLY
Figure 2.13 Circuit diagram of power supply
The above figure shows the power supply circuit. Input is given through DC
adaptor. Diode IN4007 is to avoid the polarity inversion when plugging. LED is for displaying
the status. Capacitive filters are used to eliminate ripples. 1000uF capacitor is electrolytic and
0.1uF is disc capacitor. The capacitor filter should be rated at a minimum of 1000uF for each
amp of current drawn and at least twice the input voltage. The 0.1uF capacitor eliminates any
high frequency pulses that could otherwise interfere with the operation of the regulator.
Voltage regulators are very robust. They can withstand over-current draw due to
short circuits and also over-heating. In both cases the regulator will shut down before damage
occurs. The only way to destroy a regulator is to apply reverse voltage to its input. Reverse
polarity destroys the regulator almost instantly. To avoid this possibility you should always use
diode protection of the power supply. This is especially important when using nine volt battery
supplies as it is common for people to 'test' the battery by connecting it one way and then the
other. Even this short 'test' could destroy the regulator if a protection diode is not used. Generally
a 1N4004, 1 amp power diode is connected in series with the power supply. If the supply is
connected the wrong way around, the regulator will be protected from damage.
The LM78XX series of three terminal regulators is available with several fixed
output voltages making them useful in a wide range of applications. One of these is local on card
regulation, eliminating the distribution problems associated with single point regulation. The voltages available allow these regulators to be used in logic systems, instrumentation, HiFi, and other solid state electronic equipment. Although designed primarily as fixed voltage regulators these devices can be used with external components to obtain adjustable voltages and currents. The LM78XX series is available in an aluminum TO-3 package which will allow over 1.0A load current if adequate heat sinking is provided. Current limiting is included to limit the peak output current to a safe value. Safe area protection for the output transistor is provided to limit internal power dissipation. If internal power dissipation becomes too high for the heat sinking provided, the thermal shutdown circuit takes over preventing the IC from overheating. Considerable effort was expanded to make the LM78XX series of regulators easy to use and minimize the number of external components. It is not necessary to bypass the output, although this does improve transient response. Input bypassing is needed only if the regulator is located far from the filter capacitor of the power supply.
MAX 232 Level Converter
A standard serial interfacing for PC, RS232C, requires negative logic, i.e., logic '1' is -3V to -12V and logic '0' is +3V to +12V. To convert TTL logic, say, TxD and RxD pins of the uC chips, thus need a converter chip. A MAX232 chip has long been using in many uC boards. It provides 2-channel RS232C port and requires external 10uF capacitors. Carefully check the polarity of capacitor when soldering the board. A DS275, however, no need external capacitor and smaller. Either circuit can be used without any problems. Serial RS-232 (V.24) communication works with voltages -15V to +15V for high and low. On the other hand, TTL logic operates between 0V and +5V . Modern low power consumption logic operates in the range of 0V and +3.3V or even lower.
Thus the RS-232 signal levels are far too high TTL electronics, and the negative RS-232 voltage for high can‟t be handled at all by computer logic. To receive serial data from an RS-232 interface the voltage has to be reduced. Also the low and high voltage level has to be inverted.
RS-232
TTL
Logic
-15V … -3V
+2V … +5V
High
+3V … +15V
0V … +0.8V
Low
MAX232:
This module is primary of interest for people building their own electronics with an RS-232 interface. Serial RS-232 communication works with voltages (-15V ... -3V for high ) and +3V ... +15V for low) which are not compatible with normal computer logic voltages. On the other hand, classic TTL computer logic operates between 0V ... +5V (roughly 0V ... +0.8V for low, +2V ... +5V for high). Modern low-power logic operates in the range of 0V ... +3.3V or even lower.
So, the maximum RS-232 signal levels are far too high for computer logic electronics, and the negative RS-232 voltage for high can't be grokked at all by computer logic. Therefore, to receive serial data from an RS-232 interface the voltage has to be reduced, and the low and high voltage level inverted. In the other direction (sending data from some logic over RS-232) the low logic voltage has to be "bumped up", and a negative voltage has to be generated, too. RS-232 TTL Logic ----------------------------------------------- -15V ... -3V <-> +2V ... +5V <-> high +3V ... +15V <-> 0V ... +0.8V <-> low
All this can be done with conventional analog electronics, e.g. a particular power supply and a couple of transistors or the once popular 1488 (transmitter) and 1489 (receiver) ICs. However, since more than a decade it has become standard in amateur electronics to do the necessary signal level conversion with an integrated circuit (IC) from the MAX232 family (typically a MAX232A or some clone). In fact, it is hard to find some RS-232 circuitry in amateur electronics without a MAX232A or some clone.
The MAX232 from Maxim was the first IC which in one package contains the necessary drivers (two) and receivers (also two), to adapt the RS-232 signal voltage levels to TTL logic. It became popular, because it just needs one voltage (+5V) and generates the necessary RS-232 voltage levels (approx. -10V and +10V) internally. This greatly simplified the design of circuitry. Circuitry designers no longer need to design and build a power supply with three voltages (e.g. -12V, +5V, and +12V), but could just provide one +5V power supply, e.g. with the help of a simple 78x05 voltage converter
CIRCUIT DAIGRAM TRANSMITTER
RECEIVER
PCB & CIRCUIT FABRICATION PCB FABRICATION Printed Circuit Broad (PCB) is a mechanical assembly consisting of layers of fiberglass sheet laminated with etched copper patterns. It is used to mount electronic parts in a rigid manner suitable for packaging. The type of integrated circuit components used in the fabrication process has an important role in the design of PCB. The conductor width, spacing between the signal conductors etc, are calculated to give optimum wave impedance of the conductor's lines. Optimum wave impedance gives minimum delay or rising and trailing edge of the pulse in digital circuit. Art Work Generation The generation of PCB artwork should be considered as the first step of the PCB manufacturing process. The artwork is generated at 1:1:1 or 4:1 scale according to the accuracy needed. Ink drawing on a transparent drawing paper or cut up and strip method are the methods used for the art work generation. Routing Presently artwork generation is not used for the PCB fabrication. Instead there are many types of software available for the routing of PCBs. Mainly used software‟s are CAD SOFTWARE EAGLE, ORCAD, TRAXMAKER, EASYPCB, PORTAL etc. Here we make use of CAD SOFT EAGLE. 1. Manual. Traces are placed manually as done in the traditional method where you change the path of the trace every time you click the mouse. 2. Follow-me. This highly interactive method combines the power of an auto router with the control and flexibility of manual routing. 3. Auto Router. This fully automated method will auto route an entire trace by clicking on a rats net line
Then using a laser printer solution prints the routed diagram. Laser printer is very affordable, fast and good quality. The printer used must have at least 600dpi resolution for all but the simplest PCB swill require only 300DPI resolution. It is very important that the printer produces the good solid black with no toner pinholes. When using tracing paper or drafting film, always use manual paper feed, and set the straightest possible paper output path, to keep the artwork as flat as possible and minimize jamming. The printed diagram is then converted into film by using vertically mounted cameras. Screen-printing Screen-printing is arguably the most versatile of all printing process. It can be used to print on a wide variety of substrates, including paper, paper board, plastics, glass, metals, posters, labels, decals, signage, and all types of textiles and electronic circuit boards. The advantage of screenwriting over other print processes is that the press can print on substrates of any shape, thickness and size. A significant characteristic of screen-printing is that a greater thickness of the ink can be applied to the substrate than is possible with other printing techniques. This allows for some very interesting effects that are not possible using other printing methods. Because of the simplicity of the application process, a wider range of inks and dyes are available for use in screen-printing than for use in any other printing process. Screen Printing Process Overview Screen-printing consists of three elements: the screen which is the image carrier, the squeegee; and ink. The screen-printing process uses a porous mesh stretched tightly over a frame made of wood or metal. Proper tension is essential to accurate color registration. The mesh is made of porous fabric or stainless steel mesh. A stencil is produced on the screen either manually or photo chemically. The stencil defines the image to be printed in other printing technologies this would be referred to as the image plate. Screen printing ink is applied to the substrate by placing the screen over the material. Ink with a paint-like consistency is placed on to the top of the screen. Ink is then forced through the fine mesh openings using a squeegee that is drawn across the screen, applying pressure thereby
forcing the ink through the open areas where no stencil is applied, thus forming an image on the printing substrate. The diameter of the threads and the thread count of the mesh will determine how much ink is deposited onto the substrates. Etching In all subtractive PCB process, etching is one of the most important steps. The final copper pattern is formed by selective removal of all unwanted copper, which is not protected by an etch resist. There are two basic ways that you can remove unwanted copper from copper-clad substrates to form electronic circuits: mechanical etching and chemical milling (etching). Mechanical Etching It involves the use of a precise numerically controlled multi-axis machine tool and a special milling cutter to remove a narrow strip of copper from the boundary of each pad and trace. The removal of this copper electrically isolates the circuit element from the rest of the foil. Chemical Etching It relies on the action of any one of a family of corrosive liquids to dissolve away-unwanted copper in order to define the desired circuit pattern. But in practice, factors like under-etching and overhang compliance the etching process. Under Etching During etching process etching must progress vertically. But in practice etching takes place in the sideways which attacks the pattern below the etch resist. Under etching can be minimized by keeping the etching, time as short as possible and by pressurized perpendicular discharge of the etched towards the surface to be etched. Rinsing After etching is over, the ferric chloride contaminated surface is cleaned. A simple spray water rinse is a dip in a 5% oxalic acid solution to remove the iron and copper salts.
Plating Plating of metal can be accomplished on a copper pattern by three methods: 1) Immersion plating 2) Electrolysis plating 3) Electroplating Immersion plating It is the deposition of metallic coating on a substrate, by chemical replacement, from a solution of a salt of the coating metal. Advantages of immersion plating are simplicity, minor capital expenses and increase in deposits. Tin and its alloys and gold are the two most commonly used coating metals. CIRCUIT FABRICATION AND SOLDERING DETAIL Soldering techniques Soldering is an important skill for electrical technician. Good soldering is important for proper operation of equipment. Solder is an alloy of tin and lead. The solder that is most used is 60/40 solder. This means that it is made from 60%tin and 40% lead. Solder melts at a temperature of about 400 degree Fahrenheit. For solder to adhere to join, the parts must to enough to melt the solder. Rosin flux is contained inside the solder. It is called rosin-core solder. A good mechanical joint must be made when soldering. Heat is then applied until the material rare hot. When they are hot, solder is applied to the joint. The heat of the metal parts is used to melt the solder. Only a small amount of heat should be used sparingly. The joint should appear smooth and thin. If it does not, it could be a "cold" solder joint. This is called a “cold joint". Care should be taken not to damage PCB when soldering parts on to them. Small, low wattage irons should be used with PCB and semiconductor devices
Need of flux Flux is needed for achieving desired clean lines of the surface. Most metals tend to form compounds with atmospheric oxygen, which leads a coating of oxide even at room temperature, react chemically with oxides and disperse the reaction products. Fluxes are applied before and during soldering. Soldering Tools To facilitate soldering work, various tools are necessary. The most essential tools in the soldering practice are: Soldering iron A soldering should supply sufficient heat to melt solder by heat transfer, when the iron tip is applied to the connection to the soldered. There are two general classes of soldering irons. a) Soldering pencils: Soldering pencils are lightweight soldering tools, which can generate as little as 10W or as much as SOW. A) 25W is well suited for light duty works such as soldering on PCBs. b) Soldering gun: A gun is heavier and generates more heat than the average pencils. Soldering of heavy-duty conductors requires the use of a gun because it can generate enough heat to quickly being a heavy metal joint at the proper soldering temperature. These soldering tools are called gun-soldering station. Strippers and bending tools Strippers are used to remove insulation from the wire. Bending tools are those having smooth bending surface so that they do not cause any damage to the component. Soldering techniques Soldering is an important skill for electrical technician. Good soldering is important for proper operation of equipment.
Solder is an alloy of tin and lead. The solder that is most used is 60/40 solder. This means that it is made from 60%tin and 40% lead. Solder melts at a temperature of about 400 degree Fahrenheit. For solder to adhere to join, the parts must to enough to melt the solder. Rosin flux is contained inside the solder. It is called rosin-core solder. When they are hot, solder is applied to the joint. The heat of the metal parts is used to melt the solder. Only a small amount of heat should be used sparingly. The joint should appear smooth and thin. If it does not, it could be a "cold" solder joint. This is called a “cold joint". Care should be taken not to damage PCB when soldering parts on to them. Small, low wattage irons should be used with PCB and semiconductor devices Need of flux Flux is needed for achieving desired clean lines of the surface. Most metals tend to form compounds with atmospheric oxygen, which leads a coating of oxide even at room temperature, react chemically with oxides and disperse the reaction products. Fluxes are applied before and during soldering. SOLDERING TOOLS To facilitate soldering work, various tools are necessary. The most essential tools in the soldering practice are: Soldering iron A soldering should supply sufficient heat to melt solder by heat transfer, when the iron tip is applied to the connection to the soldered. There are two general classes of soldering irons. 1. Soldering pencils: Soldering pencils are lightweight soldering tools, which can generate as little as 10W or as much as SOW. A) 25W is well suited for light duty works such as soldering on PCBs. 2. Soldering gun: A gun is heavier and generates more heat than the average pencils. Soldering of heavy-duty conductors requires the use of a gun because it can generate enough heat to quickly being a heavy metal joint at the proper soldering temperature. These soldering tools are called gun-soldering station.
ADVANTAGES
Increased Road Safety.
Reduced strain on engines, thereby increasing the life of engines.
Reduced fuel consumption.
Reduced pollution & thus improved environment.
Reduced maintenance cost for the vehicle owner(s).
CONCLUSION The project was really a novel experience for us. It will not be without some pride when we think that we have accomplished the programming, circuit testing, PCB fabrication, assembling, soldering, getting cabinet done, final product testing, etc all within a short span of time. The experience that we got during this tenure will help us to handle similar projects with ease in future. The new speed limiting system presented in this project combines several pioneering techniques that integrate wireless technologies in order to implement a reliable speed control system. This proposed system can be easily implemented near different populated areas. The power of the proposed system lies in its flexibility and capability of development with little hardware changes such as changing the speed limits and speed control methods using the software of the base station in negligible amount of time. The proposed system is based on microcontroller technology for collecting data related to speed and transmitting it through a transceiver to a base station that analyzes the transmitted data and takes appropriate decisions related to speed limit and control requirements. This experience has encouraged us to learn more about upcoming trends and technologies and thereby adding our bumble knowledge and experience about the vast ocean of electronics.
Appendix 1
REFERENCE
1. Ubald „Fundamentals Of Electronics‟
2. Dellon.T.Horn „How to test almost anything electronics‟
3. “Architecture of PIC Micro controller ”, www.microchip.com
4. http://robosoftsystems.co.in/roboshop/index.php/electronics-components/led-display/16x2-alphanumeric-lcd-hd44780 “ LCD Display”
5. http://en.wikipedia.org/wiki/555_timer_IC , “Working details of 555 Timer IC”
6. “Voltage regulator LM 7805”, http://www.national.com/search/ LM7805.html